(1) A new, simplified routine procedure for the preparation of blowfly Calliphorin has been perfected. (2) The titers of calliphorin in the larval hemolymph (blood) and tissues, in whole developing adults during metamorphosis and in adult flies have been determined. (3) Hemolymph volumes during larval growth have been estimated by C14-insulin and dye injections. The latter technique has been shown to yield erroneously high values. (4) The rates of labeled amino acid incorporation into newly synthesized protein by larval fat body in vivo as a function of larval age are entirely different when determined for the entire organ as opposed to "per mg fat body protein" due to growth of the fat body.